Proposal of "Amphixenosis" as a Classification Term for Bidirectional Human–Animal Disease Transmission

The One Health concept has increasingly emphasized the interconnectedness of human, animal, and environmental health. While cases of bidirectional human–animal disease transmission have been documented with pathogens such as SARS-CoV-2 and Streptococcus zooepidemicus, there remains no widely adopted dedicated classification term. Existing terminologies (e.g., zoonosis, reverse zoonosis, spillover, spillback, bidirectional transmission) are either broad, vague, unidirectional, event-specific, or descriptive. “Amphixenosis” may address this lack of a unified term. However, despite being a conceptually suitable descriptor, bidirectional transmission is often described under broader terminology, and the term is rarely used. To address this, our opinion piece proposes the consideration of “amphixenosis” as a dedicated term for connected bidirectional human–animal transmission while also proposing preliminary operational criteria. Greater use of a dedicated term could enhance conceptual clarity, communication, literature indexing and retrieval, and classification within One Health.